The present invention relates to a torque-measuring device.
More specifically, the invention relates to torque-measuring devices which are inserted between two coaxial drive shaft portions connecting a driving member and a driven member.
Such devices are used, for example, in motor vehicle electric window lifter assemblies or in vehicle electric sunshine roof assemblies.
It is known that one of the most important problems regarding the operation of such window lifter assemblies is their operating safety and in particular the control of their operation when any object becomes jammed between the window and the rest of the door of the vehicle.
This operation can be controlled, for example, on the basis of the rotational speed of the output shaft of the motor for driving these assemblies, of the current drawn by this motor, or alternatively of the resistive torque applied to the output shaft thereof.
The invention deals more specifically with devices of the last type.
Now, in the state of the art, torque-measuring devices are known which are inserted between two coaxial drive shaft portions connecting a driving member, such as an electric motor, and a driven member, such as a window lifter worm-and-wheel mechanism, and which include two discs arranged facing one another in planes which are more or less perpendicular to the axis of shaft portions and bearing at their periphery position-encoding means, each connected to one shaft portion and to one another by a block of elastically deformable material, while position-detecting means are arranged facing the position-encoding means of the discs.
The output of these position-detecting means is connected to means for determining torque by analysing data delivered by these position-detecting means.
It is also known that the position-encoding means and the corresponding position-detecting means may be formed of optical means or magnetic means.
In the state of the art, the position-detecting means comprise two sensors arranged facing the encoding means of the discs and the torque is determined on the basis of the output signals from these two sensors by analysing the shift between these signals, this shift resulting from a deformation of the block of elastically deformable material under the effect of the torque.
However, it will be understood that this structure has a certain number of drawbacks, especially on account of the number of parts needed and therefore the cost of producing these devices.
The purpose of the invention is therefore to solve these problems by proposing a torque-measuring device which is simple and reliable.
To this end, the subject of the invention is a torque-measuring device inserted between two coaxial drive shaft portions connecting a driving member and a driven member, of the type including two discs arranged facing one another in planes which are more or less perpendicular to the axis of the shaft portions and bearing at their periphery position-encoding means, each connected to one shaft portion and to one another by a block of elastically deformable material, and position-detecting means arranged facing the position-encoding means of the discs, the output of which is connected to torque-determining means, characterized in that the position-encoding means are formed of alternating axially projecting parts of the discs, extending facing the block of elastically deformable material, in that the position-detecting means comprise a position sensor arranged facing the alternating projecting parts and in that the torque-determining means comprise means of analysing the duty cycle of the output signals of the sensor.
Advantageously, means forming an axial spacer are arranged between the discs in the block of elastically deformable material.